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Systematic (IUPAC) name
Clinical data
Trade names Propecia, Proscar
AHFS/ monograph
MedlinePlus a698016
  • X (will cause birth defects in a fetus)
Legal status
Routes of
Pharmacokinetic data
Bioavailability 63%
Metabolism Hepatic
Biological half-life Elderly: 8 hours
Adults: 6 hours
Excretion Feces (57%) and urine (39%) as metabolites
CAS Registry Number 98319-26-7 YesY
ATC code G04CB01 D11AX10
PubChem CID: 57363
DrugBank DB01216 YesY
ChemSpider 51714 YesY
KEGG D00321 YesY
Chemical data
Formula C23H36N2O2
Molecular mass 372.549 g/mol
 YesY (what is this?)  (verify)

Finasteride (INN, USAN, BAN) (brand names Proscar, and Propecia by Merck, among other generic names; former developmental code name MK-906) is a drug used for the treatment of benign prostatic hyperplasia (BPH) and male pattern baldness (MPB).[1][2] It is a type II and type III 5α-reductase inhibitor;[3] 5α-reductase, an enzyme, converts testosterone to dihydrotestosterone (DHT).[2]

Medical uses

Benign prostatic hyperplasia

Physicians use finasteride for the treatment of BPH, informally known as an enlarged prostate. Finasteride may improve the symptoms associated with BPH such as difficulty urinating, getting up during the night to urinate, hesitation at the start of urination, and decreased urinary flow. It provides less symptomatic relief than alpha-1 blockers such as tamsulosin and symptomatic relief is slower in onset (six months or more of treatment with finasteride may be required to determine the therapeutic results of treatment). Symptomatic benefits are mainly seen in those with prostate volume > 40 cm2. In long-term studies finasteride but not alpha-1 inhibitors reduce the risk of acute urinary retention (-57% at 4 years) and the need for surgery (-54% at 4 years). If the drug is discontinued, any therapeutic benefits reverse within about 6–8 months.[4][5][6]

Male pattern baldness

Finasteride is used to treat male pattern hair loss (androgenetic alopecia) in men only.[7] Treatment provides about 30% improvement in hair loss after six months of treatment, and effectiveness only persists as long as the drug is taken.[8]

Off-label uses

Finasteride is sometimes used in hormone replacement therapy for male-to-female transsexuals in combination with a form of estrogen due to its antiandrogen properties. However, little clinical research of finasteride use for this purpose has been conducted and evidence of efficacy is limited.[9]


Finasteride is not approved for use in women, especially due to risks of birth defects in a fetus. It is classified in the FDA pregnancy category X.[7]

Adverse effects

Adverse effects from finasteride are rare.[4] The FDA has added a warning to 5α-reductase inhibitors concerning an increased risk of high-grade prostate cancer, as the treatment of BPH lowers PSA, which could mask the development of prostate cancer.[10][11]

Although overall incidence of male breast cancer in clinical trials for finasteride 5 mg was not increased, there are post-marketing reports of breast cancer in association with its use. Available evidence does not provide clarity as to whether there is a causative relationship between finasteride and these cancers.[7][12]

The effect of finasteride on sexual function is controversial. There are case reports of persistent diminished libido or erectile dysfunction after stopping the drug and the FDA has updated the label to inform healthcare professionals of these reports.[8][13] A 2010 review found moderate quality evidence that finasteride increased the risk of sexual dysfunction, but not of discontinuing treatment due to sexual side effects.[14]

A 2015 meta analysis found none of the clinical trials had adequate safety reporting and did not provide sufficient information to establish the safety profile for finasteride's treatment of hairloss. The study concluded the existing clinical trials of finasteride for hair loss provide very limited information on toxicity, are of poor quality, and seem to be systematically biased toward under detection of adverse events. Moreover, the trials submitted to the FDA for approval for hair loss excluded most men who would normally be prescribed finasteride for androgenic alopecia.[15][16]

When finasteride was originally approved for hair loss in 1997, the FDA approval review reported that it appears well tolerated, with the most common side effects being related to sexual function.[17] In many people these side effects resolve if the medication is stopped and occasionally resolve even if the medication is continued.[17] They additionally state "the sexual functioning questionnaire seems to have given a sensitive reflection of the disturbance on sexual functioning".[17]

Mechanism of action

Finasteride is a 5α-reductase inhibitor, specifically the type II and III isoenzymes.[3][18] By inhibiting 5α-reductase, finasteride prevents conversion of testosterone to dihydrotestosterone (DHT) by the type II and III isoenzymes, resulting in a decrease in serum DHT levels by about 65–70% and in prostate DHT levels by up to 85–90%,[3][19] where expression of the type II isoenzyme dominates. Unlike triple inhibitors of all three isoenzymes of 5α-reductase like dutasteride which can reduce DHT levels in the entire body by more than 99%,[3] finasteride does not completely suppress DHT production because it lacks significant inhibitory effects on the 5α-reductase type I isoenzyme, with 100-fold less affinity for I as compared to II.[7] In addition to blocking the type II and III isoenzymes, finasteride competitively inhibits the 5β-reductase type II isoenzyme,[20] though this is not believed to affect androgen metabolism.

By blocking DHT production, finasteride reduces androgen activity in the scalp. In the prostate, inhibition of 5α-reductase reduces prostate volume, which improves BPH and reduces risk of prostate cancer. Inhibition of 5α-reductase also reduces epididymal weight, and decreases motility and normal morphology of spermatozoa in the epididymis.[21]

DHT helps activate the GABAA receptor, which functions to tamp down signaling among neurons; because finasteride prevents the formation of DHT, it may contribute to a reduction of GABAA activity. Reduced GABAA has been implicated in depression, anxiety, and sexual dysfunction.[22][23][24]

Physical and chemical properties

Finasteride is a 4-azasteroid analogue of testosterone and is lipophilic.[25]

Drug trade names include Propecia and Proscar, the former marketed for male pattern baldness (MPB) and the latter for benign prostatic hyperplasia (BPH), both are products of Merck & Co. There is 1 mg of finasteride in Propecia and 5 mg in Proscar. Merck's patent on finasteride for the treatment of BPH expired on June 19, 2006.[26] Merck was awarded a separate patent for the use of finasteride to treat MPB. This patent expired in November 2013.[27]


In 1974, Julianne Imperato-McGinley of Cornell Medical College in New York attended a conference on birth defects. She reported on a group of intersex children in the Caribbean who appeared sexually ambiguous at birth, and were initially raised as girls, but then grew external male genitalia and other masculine characteristic after onset of puberty. Her research group found these children shared a genetic mutation, causing deficiency of the 5α-reductase enzyme and male hormone dihydrotestosterone (DHT), which was found to have been the etiology behind abnormalities in male sexual development. Upon maturation, these individuals were observed to have smaller prostates which were underdeveloped, and were also observed to lack incidence of male pattern baldness.[28][29]

In 1975, copies of Imperato-McGinley's presentation were seen by P. Roy Vagelos, who was then serving as Merck's basic-research chief. He was intrigued by the notion that decreased levels of DHT led to the development of smaller prostates. Dr. Vagelos then sought to create a drug which could mimic the condition found in these children to treat older men who were suffering from benign prostatic hyperplasia.[30]

In 1992, finasteride (5 mg) was approved by the U.S. Food and Drug Administration (FDA) for treatment of BPH, which Merck marketed under the brand name Proscar.

In 1997, Merck was successful in obtaining FDA approval for a second indication of finasteride (1 mg) for treatment of MPB, which was marketed under the brand name Propecia.

Society and culture

In 2005, the World Anti-Doping Agency banned finasteride because a laboratory in Germany discovered the drug could be used to mask steroid abuse.[31] It was removed from the list effective January 1, 2009, after improvements in testing methods made the ban unnecessary.[32] Notable athletes who used finasteride for hair loss and were banned from international competition include skeleton racer Zach Lund, bobsledder Sebastien Gattuso, footballer Romário and ice hockey goaltender José Théodore.[32][33]

In 2012, an advocacy group called the Post-Finasteride Syndrome Foundation was formed; the group "coined the phrase 'post finasteride syndrome' which they say is characterised by sexual, neurological, hormonal and psychological side effects that can persist in men who have taken finasteride for hair loss or an enlarged prostate".[34][35]


Finasteride has been clinically tested for baldness in women; the results were no better than placebo.[36]

See also


  1. ^ J. Buckingham (1987). Dictionary of Organic Compounds. CRC Press. p. 3147. ISBN 978-0-412-54090-5. 
  2. ^ a b I.K. Morton; Judith M. Hall (6 December 2012). Concise Dictionary of Pharmacological Agents: Properties and Synonyms. Springer Science & Business Media. pp. 121, 246. ISBN 978-94-011-4439-1. 
  3. ^ a b c d Yamana K, Labrie F, Luu-The V (January 2010). "Human type 3 5α-reductase is expressed in peripheral tissues at higher levels than types 1 and 2 and its activity is potently inhibited by finasteride and dutasteride". Hormone Molecular Biology and Clinical Investigation 2 (3). doi:10.1515/hmbci.2010.035. 
  4. ^ a b Tacklind, J; Fink, HA; Macdonald, R; Rutks, I; Wilt, TJ (Oct 6, 2010). "Finasteride for benign prostatic hyperplasia.". The Cochrane database of systematic reviews (10): CD006015. doi:10.1002/14651858.CD006015.pub3. PMID 20927745. 
  5. ^ Proscar label
  6. ^ "Treatment of Non-neurogenic Male LUTS | Uroweb". 
  7. ^ a b c d "Propecia label" (PDF). 
  8. ^ a b Varothai, S; Bergfeld, WF (Jul 2014). "Androgenetic alopecia: an evidence-based treatment update.". American journal of clinical dermatology 15 (3): 217–30. doi:10.1007/s40257-014-0077-5. PMID 24848508. 
  9. ^ Knezevich EL, Viereck LK, Drincic AT (January 2012). "Medical management of adult transsexual persons". Pharmacotherapy 32 (1): 54–66. doi:10.1002/PHAR.1006. PMID 22392828. 
  10. ^ FDA. Posted 9 June 2011. 5-alpha reductase inhibitors (5-ARIs): Label Change - Increased Risk of Prostate Cancer
  11. ^ Walsh PC (April 2010). "Chemoprevention of prostate cancer". The New England Journal of Medicine 362 (13): 1237–8. doi:10.1056/NEJMe1001045. PMID 20357287. 
  12. ^ Medicines and Healthcare products Regulatory Agency Drug Safety Update. December 2009 Finasteride: potential risk of male breast cancer
  13. ^ FDA (11 April 2012). "Questions and Answers: Finasteride Label Changes". US FDA. Retrieved 26 October 2014. 
  14. ^ Mella, JM; Perret, MC; Manzotti, M; Catalano, HN; Guyatt, G (October 2010). "Efficacy and safety of finasteride therapy for androgenetic alopecia: a systematic review.". Archives of Dermatology 146 (10): 1141–50. doi:10.1001/archdermatol.2010.256. PMID 20956649. 
  15. ^ Belknap, SM; Aslam, I; Kiguradze, T; Temps, WH; Yarnold, PR; Cashy, J; Brannigan, RE; Micali, G; Nardone, B; West, DP (1 April 2015). "Adverse Event Reporting in Clinical Trials of Finasteride for Androgenic Alopecia: A Meta-analysis.". JAMA dermatology. doi:10.1001/jamadermatol.2015.36. PMID 25830296. 
  16. ^ Moore, TJ (1 April 2015). "Finasteride and the Uncertainties of Establishing Harms.". JAMA dermatology. PMID 25831198. 
  17. ^ a b c FDA. "Summary of Key Safety Findings" (PDF). p. 98. 
  18. ^ Aggarwal S, Thareja S, Verma A, Bhardwaj TR, Kumar M (February 2010). "An overview on 5alpha-reductase inhibitors". Steroids 75 (2): 109–53. doi:10.1016/j.steroids.2009.10.005. PMID 19879888. 
  19. ^ Bartsch G, Rittmaster RS, Klocker H (April 2000). "Dihydrotestosterone and the concept of 5alpha-reductase inhibition in human benign prostatic hyperplasia". European Urology 37 (4): 367–80. doi:10.1159/000020181. PMID 10765065. 
  20. ^ Drury JE, Di Costanzo L, Penning TM, Christianson DW (July 2009). "Inhibition of human steroid 5beta-reductase (AKR1D1) by finasteride and structure of the enzyme-inhibitor complex". The Journal of Biological Chemistry 284 (30): 19786–90. doi:10.1074/jbc.C109.016931. PMC 2740403. PMID 19515843. 
  21. ^ Robaire B, Henderson NA (May 2006). "Actions of 5alpha-reductase inhibitors on the epididymis". Molecular and Cellular Endocrinology 250 (1-2): 190–5. doi:10.1016/j.mce.2005.12.044. PMID 16476520. 
  22. ^ Finn DA, Beadles-Bohling AS, Beckley EH; et al. (2006). "A new look at the 5alpha-reductase inhibitor finasteride". CNS Drug Reviews 12 (1): 53–76. doi:10.1111/j.1527-3458.2006.00053.x. PMID 16834758. 
  23. ^ Römer B, Gass P (December 2010). "Finasteride-induced depression: new insights into possible pathomechanisms". Journal of Cosmetic Dermatology 9 (4): 331–2. doi:10.1111/j.1473-2165.2010.00533.x. PMID 21122055. 
  24. ^ Gunn BG, Brown AR, Lambert JJ, Belelli D (2011). "Neurosteroids and GABA(A) Receptor Interactions: A Focus on Stress". Frontiers in Neuroscience 5: 131. doi:10.3389/fnins.2011.00131. PMC 3230140. PMID 22164129. 
  25. ^ Azeem A, Khan ZI, Aqil M, Ahmad FJ, Khar RK, Talegaonkar S (May 2009). "Microemulsions as a surrogate carrier for dermal drug delivery". Drug Development and Industrial Pharmacy 35 (5): 525–47. doi:10.1080/03639040802448646. PMID 19016057. 
  26. ^ Primary Patent Expirations for Selected High Revenue Drugs
  27. ^ | Patent Expiration for Propecia
  28. ^ Imperato-McGinley J, Guerrero L, Gautier T, Peterson RE (December 1974). "Steroid 5alpha-reductase deficiency in man: an inherited form of male pseudohermaphroditism". Science 186 (4170): 1213–5. doi:10.1126/science.186.4170.1213. PMID 4432067. 
  29. ^ Emerick JE et al. for WebMD. Last Updated Updated: 29 May 2014 5-Alpha-Reductase Deficiency
  30. ^ Freudenheim, Milt (February 16, 1992). "Keeping the Pipeline Filled at Merck". The New York Times. 
  31. ^ Sandomir, Richard (2006-01-19). "Skin Deep; Fighting Baldness, and Now an Olympic Ban". The New York Times. Retrieved 2010-05-02. 
  32. ^ a b Staff, The Australian. 28 October 2008 WADA removes Finasteride from ban list
  33. ^ Staff, Sydney Morning Herald. 9 October 2008 WADA takes Romario's drug off banned list
  34. ^ Jill Margo for the Australian Financial Review. 26 Sept 2012 Looking at care with a critical eye
  35. ^ Post-Finasteride Syndrome Foundation official website
  36. ^ Levy, LL; Emer, JJ (Aug 29, 2013). "Female pattern alopecia: current perspectives.". International journal of women's health 5: 541–56. doi:10.2147/IJWH.S49337. PMC 3769411. PMID 24039457. 

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